RF signal processors typically require automatic gain control (AGC) in order to detect and process RF signals that may vary over a wide range of signal strength. Radar and communications receiver systems generally include (1) an antenna, either directional or omnidirectional, (2) a superheterodyne receiver for tuning to a specific RF and converting to an intermediate frequency (IF), (3) a processor for detecting IF signals and for extracting information from these, and (4) a graphical user interface.
Regarding (3), the IF signal detecting and processing component, historically the IF signal has been processed by a combination of analog and digital components. However, recent advancements in technology have allowed direct digitizing of the IF signal using an analog to digital converter (ADC), resulting in a simpler system architecture that may be termed “Direct Digitization Technology” (DDT) which eliminates the bulky and expensive analog components. For example, U.S. Pat. No. 5,161,170 describes a pulse-to-pulse AGC circuit for digital radar intercept receivers. The system, however, includes certain analog components, e.g. a logarithmic amplifier/detector and a track/hold device, and has the above-noted disadvantages regarding such analog-based designs.
Although DDT reduces system size and cost, typical RF receivers have dynamic ranges in excess of 60 dB, whereas currently available ADCs have usable dynamic ranges of 25 to 45 dB. Therefore, it is desirable to include an automatic gain control (AGC) circuit in front of the ADC to continuously adjust the signal level to be within the dynamic range of the ADC.
U.S. Pat. No. 5,276,685 shows an example of a digital design that implements AGC in a digital quadrature RF receiver. Although the system utilizes digital instead of analog components, these are selected for implementation in a personal communications system (PCS) receiver and are not optimized or well-suited for detecting and processing radar signals.
Another digital system described in U.S. Pat. No. 6,191,725 is directed to an AGC circuit for processing radar signals. The circuit utilizes digital components but requires multiple analog to digital converters (ADCs) operating in parallel to accomplish AGC, increasing the cost and the complexity of the system.
There is, therefore, a need for a digitized RF detection and processing system with fewer components, less complexity, and decreased cost.